The present invention relates to inorganic coating compositions based on cyclic carbosiloxanes, inorganic polycondensates and xcex1,xcfx89-functional linear oligosiloxanes, and also to a process for production thereof and to the use thereof and to a non-stick coating so obtained.
Inorganic coatings based on siloxane have been state of the art for a long time and are valued in many fields on account of their properties. Silicone-resin lacquers, which are substantially composed of randomly distributed T, D and M units and, in part, also of Q units, are produced from the corresponding chlorosilanes with the aid of direct or indirect hydrolysis. The step of hydrolysis of the silanes to form oligosiloxanes is followed by the step of condensation to form organopolysiloxane resins, so-called xe2x80x9cbodyingxe2x80x9d. The production processes are described, for example, in W. Noll, Chemie und Technologie der Silicone, VCH-Verlag, 1968 and in Chemie in Unserer Zeit, 23, (1989), 86-99. The technology and properties of silicone resins are also summarised therein. Hard, mechanically loadable though brittle coatings can be produced, in particular, with pure methyl-silicone resins. In order to obtain the final properties, silicone-resin lacquers have to be baked at temperatures from 180 to 230xc2x0 C.
In contrast with the production of silicone resin, in the case of the sol-gel process an oligosiloxane sol is produced by hydrolysis and polycondensation of alkoxysilanes without subsequent xe2x80x9cbodyingxe2x80x9d. In comparison with silicone resins, the sols have a much larger number of reactive SiOH or SiOR groups and possess a higher crosslinkage density by virtue of a higher proportion of Q units. Sol-gel coating systems have the known positive properties of the silicon resins, such as high thermal stability, resistance to solvents and to many liquids in daily use, non-stick action and resistance to weathering. By reason of their higher reactivity and crosslinkage density, sol-gel coatings can be cured at lower temperatures from about 80xc2x0 C. to about 130xc2x0 C., and they surpass silicone-resin lacquers in hardness and mechanical stability.
The disadvantage of condensation-crosslinking sol-gel coating systems is their lower solids content or, to be more exact, their high VOC content. The solids content of sol-gel lacquers lies, as a rule, between 10 and 50 wt. %, generally around a maximum of 30 wt. %. However, the reduction of volatile organic compounds (VOC) is being demanded to an increasing extent by the coating industry. A further disadvantage of the existing sol-gel coating systems is their tendency to crack by reason of low flexibility. They can therefore only be applied in slight layer thicknesses of a few xcexcm. In addition, for many applications, such as for example for providing protection against graffiti on buildings, large vehicles and rail vehicles, it would be advantageous if inorganic sol-gel systems obtained their properties already in the course of curing at room temperature.
A demand therefore exists for inorganic sol-gel systems without the disadvantages stated above but with the stated advantages.
The state of the art consists in varying the flexibility and hardness of sol-gel lacquers within certain limits via the type and the quantitative ratios of the silanes and additives that are employed for producing the coating composition. In U.S. Pat. No. 4,624,870 methyltrialkoxysilane is hydrolysed with colloidal SiO2. The properties are controlled via the ratio of CH3SiO3/2 units to SiO2 units. U.S. Pat. Nos. 3,986,997, 4,027,073 and EP-A 358 011 describe the (co)hydrolysis of organofunctional alkyltrialkoxysilanes such as methyltrialkoxysilane, glycidyloxypropyltrialkoxysilane or methacryloxypropyltrialkoxysilane and tetraethoxysilane (TEOS) as well as, optionally, inorganic nanoparticles. With these systems the properties can be controlled via the type and proportion of the organofunctional silanes with respect to the overall composition. In U.S. Pat. No. 4,324,712 the tendency of the coating composition to crack is reduced by addition of 0.5 to 5% of a linear functional oligosiloxane to the (co)hydrolysate formed from alkyltrialkoxysilane and colloidal SiO2. In PCT patents 8/52992 and 94/06807 multifunctional, preferably cyclic, organosiloxanes are employed for the modification of inorganic coatings.
Also state of the art is the hydrophobic and/or oleophobic modification of the previously described coating compositions by addition of fluorine-containing components, fluorine-containing alkoxysilanes being preferred. Such coatings are distinguished by good non-stick properties and are described, for example, in DE-A 41 18 184 and in WO 99/03941.
However, all the condensation-crosslinking sol-gel systems known in accordance with the state of the art exhibit at least one of the disadvantages stated at the outset, ruling out extended use in many fields.
The object of the present invention was therefore to make available an inorganic solgel coating that does not exhibit the disadvantages described previously. A further object of the invention consisted in making available a suitable process for production of the coating composition according to the invention.
The invention is based on the surprising observation that coating compositions that achieve the object underlying the invention can be obtained through the combination of cyclic carbosilanes and/or carbosiloxanes, inorganic polycondensates and xcex1,xcfx89-functional linear oligosiloxanes.
The invention consequently provides coating compositions containing
I) a multifunctional carbosilane and/or carbosiloxane of the general formula (I)
W[(CH2)mSiR1nX(3xe2x88x92n)]pxe2x80x83xe2x80x83(I)
xe2x80x83and/or the (partial) condensation product thereof with
R1 C1-C18 alkyl and/or C6-C20 aryl, where R1 within the molecule may be the same or different,
X a residue selected from the group consisting of OH, C1-C4 alkoxy, C6-C20 aryloxy, C1-C6 acyloxy, preferably OH, methoxy or ethoxy,
n 0 to 2
m 2 to 6
p integerxe2x89xa72 and
W either a linear, cyclic or branched silane or siloxane,
II) a polycondensation product of one or more hydrolysable compounds of the general formula (II)
R2aM(Y)(b)xe2x80x83xe2x80x83(II)
xe2x80x83with
M Si, B, Al, Ti, Zr, V, Zn, preferably Si
R2 the same or different non-hydrolysable C1-C14 alkyl residues or C6-C20 aryl residues, which may be replaced by at least one member of the group consisting of O, N, S, P,
Y a hydrolysable group, preferably C1-C8 alkoxy or C2-C8 acyloxy, C1-C2 alkoxy being quite particularly preferred,
a 0 to 3, preferably 0 or 1
b 1 to 4, where a+b is equal to 3 or 4
and a solids content of at least 40 wt. %, preferably of at least 50 wt. %, in an OH-functional solvent,
(III) an xcex1,xcfx89-functional linear oligosiloxane of the general formula (III) 
xe2x80x83with
Z hydroxy or C1-C4 alkoxy
R3 C1-C18 alkyl or alkenyl, where R3 within the molecule may be the same or different,
c 1 to 60, preferably 3 to 25,
IV) catalysts selected from the group consisting of the acidic, basic or metallic catalysts, preferably from the group consisting of the acids such as hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, acetic acid or formic acid,
as well as, optionally,
V) inorganic fillers and/or inorganic nanoparticles, as well as
VI) conventional auxiliary substances pertaining to coating technology.
The coating composition according to the invention exhibits a solvent content of at most 50 wt. %, preferably of at most 40 wt. %. It can be applied in flawless manner in dry-layer thicknesses of clearly more than 30 xcexcm and cures at room temperature. The cured films are transparent and flexible. They are hydrophobic and possess good non-stick properties.
Suitable multifunctional carbosilanes and/or carbosiloxanes of the general formula (I) in the sense of the invention are silanes of the general formula (IV)
R44xe2x88x92pSi[(CH2)mSiR1nX3xe2x88x92n]pxe2x80x83xe2x80x83(IV)
or the (partial) condensation product thereof, with
R1 C1-C18 alkyl and/or C6-C20 aryl, where R1 within the molecule may be the same or different,
R4 C1-C18 alkyl and/or C6-C20 aryl,
X a residue selected from the group consisting of OH, C1-C4 alkoxy, C6-C20 aryloxy, C1-C6 acyloxy, preferably OH, methoxy or ethoxy,
m 2 to 6
n 0 to 2 and
p 4, 3 or 2.
In another embodiment of the invention, multifunctional carbosilanes and/or carbosiloxanes of the general formula (I) are siloxanes in which W is composed of at least two structural units selected from monofunctional units M or difunctional units D as well as, to a small extent in addition, trifunctional units T or tetrafunctional units Q and/or the condensation products and/or (partial) condensation products thereof.
The siloxanes according to the invention preferably exhibit a molecular weight (number average) between 300 and 5,000.
In a preferred embodiment of the invention the multifunctional carbosilane and/or carbosiloxane of the general formula (I) is a cyclic siloxane of the general formula (V) 
and/or the (partial) condensation product thereof with
R1 C1-C18 alkyl and/or C6-C20 aryl, where R1 within the molecule may be the same or different,
X a residue selected from the group consisting of OH, C1-C4 alkoxy, C6-C20 aryloxy, C1-C6 acyloxy, preferably OH, methoxy or ethoxy,
d 3 to 6, preferably 4
n 0 to 2
m 2 to 6.
In a particularly preferred embodiment of the coating composition according to the invention the multifunctional carbosilane and/or carbosiloxane is a compound of the formula (VI) and/or (VII) or the (partial) condensation product thereof. 
with d equal to 3, 4, 5 or 6, preferably 4.
Condensation products and (partial) condensation products are to be understood to mean oligomers or polymers that are formed from at least two molecules of the general formula (I), optionally after hydrolysis and subsequent condensation of the group X, accompanied by formation of a Sixe2x80x94Oxe2x80x94Si bond.
Several multifunctional carbosilanes and/or carbosiloxanes of the general formula (I) may also be contained in the coating composition according to the invention.
Hydrolysable compounds of the general formula (II) are preferably alkoxysilanes R2aSi(Y)(b) (with a preferably 0 or 1 and where R2, Y have the meaning stated previously in connection with formula (II)) or mixtures thereof. Particularly preferred alkoxysilanes are tetraethoxysilane, methyltriethoxysilane and/or phenyltriethoxysilane.
Preferred xcex1,xcfx89-functional linear oligosiloxanes of the general formula (III) are hydroxy-terminated polydimethyl siloxanes, those having an OH content from 0.8 to 9 being particularly preferred.
The present invention likewise provides polycondensation products formed from hydrolysable compounds of the general formula (II) and an xcex1,xcfx89-functional linear oligosiloxane of the general formula (III). In this case, alkoxysilanes R2aSi(Y)(b) (with a preferably 0 or 1 and where R2, Y have the meaning specified previously in connection with formula (II)) or mixtures thereof are preferably employed as hydrolysable compounds of the general formula (II), tetraethoxysilane being particularly preferred. It is also possible to incorporate only a part of the xcex1,xcfx89-functional linear oligosiloxane contained in the coating composition into the polycondensation product and to add the remaining portion as a separate component.
The polycondensation products contained in the coating composition according to the invention exhibit a solids content of at least 40 wt. %, preferably of at least 50 wt. %. By way of solvent, OH-functional solvents with a boiling-point higher than 110xc2x0 C. and a flash-point of at least 30xc2x0 C. are preferred. Suitable solvents are, for example, 1-butanol, 1-pentanol, 2-pentanol, 1-methoxy-2-propanol or diacetone alcohol.
By way of catalysts, use may be made of all condensation catalysts known in silicone chemistry, such as are described, for example, in W. Noll, Chemie und Technologie der Silicone, VCH-Verlag, Weinheim, 1968. Suitable catalysts are, for example, organic metallic compounds such as salts of carboxylic acid, alcoholates and phenolates, complex compounds of chelate character, basic catalysts such as alkali hydroxides, amines, alkali silanolates, quaternary ammonium hydroxides and acidic catalysts. Acidic catalysts may be Lewis acids or protonic acids such as hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, acetic acid or formic acid. The catalyst is preferably an acid, para-toluenesulfonic acid being particularly preferred. The catalyst may also be employed in the form of a solution, preferably in the same solvent that is already contained in the composition.
Further components may also be admixed to the coating composition according to the invention. For example, inorganic fillers or inorganic nanoparticles may be added by way of component (V). To a person skilled in the art it is known that as a result of the addition of inorganic nanoparticles such as, for example, metallic or semimetallic oxides or hydrated oxides of the elements Si, Al or Ti the mechanical properties of coatings are improved. Conventional auxiliary substances pertaining to coating technology may also be added by way of component (VI). Conventional auxiliary substances are all the added substances that are known for producing lacquers and paints, such as, for example, inorganic and/or organic pigments, lacquer additives such as dispersing agents, flow-control agents, thickening agents, defoaming agents and other auxiliaries, adhesive agents, fungicides, bactericides, stabilisers or inhibitors. When using the coating composition according to the invention as, for example, a non-stick coating for protection against marine fouling, customary auxiliaries also include the release or slip additives known from the prior art. These are usually hydrophobic, non-functional additives which diffuse to the boundary surface of the coating during its service life and reduce its surface tension. Suitable release or slip additives are for example silicone oils, organic oils, waxes, paraffins or paraffin jellies. It is of course also possible to add a mixture of the aforementioned components.
In a preferred embodiment of the invention the coating composition according to the invention contains
I. 20 to 70 wt. % of a multifunctional carbosilane and/or carbosiloxane of the general formula (I), preferably a compound of the formula (V) and/or (VI) or the (partial) condensation products thereof,
II. 10 to 70 wt. % of a polycondensation product of one or more hydrolysable compounds of the general formula (II), preferably of at least one hydrolysable Si compound, particularly preferably tetraethoxysilane, and/or methyltriethoxysilane and/or phenyltriethoxysilane with a solids content of at least 40 wt. %, preferably of at least 50 wt. %, in an OH-functional solvent, whereby the polycondensation product may also contain xcex1,xcfx89-functional linear oligosiloxanes,
III. 5 to 50 wt. % of an xcex1,xcfx89-functional linear oligosiloxane of the general formula (III), whereby the latter may be wholly or partially contained in the polycondensation product formed from one or more hydrolysable compounds of the general formula (II),
IV. 0.5 to 20 wt. % of a catalyst solution, preferably para-toluenesulfonic acid, dissolved in an organic solvent,
with the proviso that components (I) to (IV) add up to 100 wt. %, as well as, optionally,
V. inorganic fillers and/or inorganic nanoparticles as well as
VI. conventional auxiliary substances pertaining to coating technology
in the quantities that are conventional in coating technology. The expression xe2x80x9cquantities that are conventional in coating technologyxe2x80x9d is to be understood to mean a ratio of components (V) and (VI) to components (I) to (IV) of no more than 1:1.
An advantage of the coating composition according to the invention is that the components (I) to (IV) at least contained in the coating composition are miscible with one another in any arbitrary ratio within the limits according to the invention. The properties of the coatings that can be produced from the coating composition can consequently be adapted to the particular requirements in simple manner by varying the individual components. By increasing the proportion of xcex1,xcfx89-functional linear oligosiloxane, the flexibility and the hydrophobicity can be raised. An increased proportion with respect to polycondensation products of hydrolysable compounds of the general formula (II) improves the mechanical properties of the coating.
Since components (I), (II) and (III) of the coating composition contain hydrolysable and condensable groups, the components in the fully cured coating differ in their structure and in their percentage proportion from the coating composition employed for production of the coating.
The invention further provides a process for production of the coating composition according to the invention, characterised in that in the first process step a polycondensation product formed from hydrolysable compounds of the general formula (II) and optionally xcex1,xcfx89-functional linear oligosiloxane of the general formula (III) in an OH-functional solvent having a solids content of at least 40 wt. %, preferably of at least 50 wt. %, is produced by means of a gel-sol process, and in a second process step the polycondensation product produced in the first process step from component (II) and optionally (III) is homogeneously stirred together with the components (I), optionally (III) and (IV) as well as the other components (V) and (VI).
Multifunctional carbosilanes and/or carbosiloxanes of the general formula (I), in which W is composed of at least two units selected from monofunctional units M or difunctional units D as well as to a minor extent additionally trifunctional units T or tetrafunctional units Q and/or condensation and/or (partial) condensation products thereof can generally be obtained via two synthetic routes. In one synthetic route hydrogen-functional silanes or siloxanes are used as the starting compound W. In the other route vinyl-functional silanes or siloxanes are used as the starting compound W. Suitable hydrogen- or vinyl-functional silanes and siloxanes are commercially available or can be produced from the suitable silanes or siloxanes by direct or indirect hydrolysis or equilibration processes known in silicone technology. In the case of a hydrogen-functional starting compound W the [(CH2)mSiR1nX(3xe2x88x92n)] group according to the general formula (I) is added to W as a corresponding alkenyl-functional silane using platinum catalysis. If a vinyl-functional silane or siloxane is used as the starting compound W a corresponding hydrogen silane is used. If necessary, the radical X can then be introduced in a subsequent process step by direct or indirect hydrolysis known to the skilled man. The synthetic principle is explained in more detail in EP-A 866086, WO 94/06 807 and DE-A 196 03 241.
The production of multifunctional carbosilanes of the general formula (IV) is described in EP-A 743 313, for example; multifunctional carbosiloxanes of the formula (V) and (VI) are preferably obtainable in accordance with the processes described in EP-A 866 086, DE-A 196 03 241 and WO/98/52992.
The production, according to the invention, of the polycondensation product formed from hydrolysable compounds of the general formula (II) is effected in such a manner that, in the first process step, the hydrolysable compounds of the general formula (II) are hydrolysed and condensed by addition of water, and catalyst as well as, optionally, solvent in the manner that is conventional in sol-gel technology. For the hydrolysis it is particularly advantageous if the molar ratio of added water to hydrolysable groups Y lies within the range from 0.3:1 to 0.7:1, preferably within the range from 0.45:1 to 0.55:1. By way of catalyst, preferably between 250 and 1,000 ppm of an acid are admixed, relative to the reaction mixture. After completion of the reaction the polycondensation product is neutralised with a base, and an OH-functional solvent with a boiling-point higher than 110xc2x0 C. and a flash-point of at least 30xc2x0 C. is added. Suitable solvents are, for example, 1-butanol, 1-pentanol, 2-pentanol, 1-methoxy-2-propanol or diacetone alcohol. Then distillation is carried out up to the required solids content of at least 40% by weight, preferably at least 50% by weight. The salt that has arisen as a result of neutralisation is filtered off.
Another embodiment of the process according to the invention is the production of a polycondensation product from, preferably, alkoxysilanes R2aSi(Y)(b) (with a preferably 0 or 1, and where R2, Y have the meaning stated previously in connection with formula (II)) or mixtures thereof, particularly preferably from tetraethoxysilane and an xcex1,xcfx89-functional linear oligosiloxane. The complete quantity or only a part of the xcex1,xcfx89-functional linear oligosiloxane contained in the coating composition may be employed in the course of production of the polycondensation product. It is advantageous to dilute the mixture of alkoxysilanes R2aSi(Y)(b) and xcex1,xcfx89-functional linear oligosiloxane with a solvent, preferably with ethanol. Hydrolysis and condensation are effected in the manner that is conventional in sol-gel technology. However, it has proved to be advantageous if, after neutralisation and addition of the higher-boiling solvent, further stirring is effected for at least 60 minutes, preferably at elevated temperature. No change in the remaining parameters of the process or in the processing of the product occurs as a result of the addition of xcex1,xcfx89-functional linear oligosiloxane.
Surprisingly, the polycondensation products that are produced by the process according to the invention from the preferred alkoxysilanes R2aSi(Y)(b) and optionally xcex1,xcfx89-functional linear oligosiloxane are clear solutions or dispersions, despite the high solids content of at least 40 wt. %, preferably of at least 50 wt. %, and are storable at room temperature over a period of several months.
In the process according to the invention the components contained in the coating composition can be stirred together with one another immediately prior to application. In a preferred embodiment of the process according to the invention a 2-component formulation that is stable in storage can be produced from components (I) to (IV) according to the invention as well as, optionally, further components (V) and/or (VI). In this case it is preferred if the multifunctional carbosilane and/or carbosiloxane of the general formula (I) is a cyclic siloxane of the general formula (V) in which X is a methoxy or ethoxy residue. For example, a mixture can be produced from components (I), (II) and (III) which is stable in storage and into which, prior to application, component (IV) is worked by means of methods that are conventional in coating technology.
The invention further provides the use of the coating composition according to the invention for the production of coatings on inorganic or organic materials or objects.
The invention likewise provides non-stick layers that are obtained by application of the coating composition according to the invention onto inorganic or organic materials or objects in order to protect the latter effectively against dirt, graffiti or marine vegetation.
Surfaces, such as for example those of buildings, large vehicles and rail vehicles, can be provided with effective and lasting protection, so that they can be freed from graffiti by simple means without any residues remaining on the underlying surface and without any damage to the latter. On painted surfaces, such as for example those of underground trains or trams or local trains the coating composition according to the invention can be applied to the topcoat as an additional protective layer. In the case of absorbent underlying mineral surfaces, such as for example is frequently the case with buildings, it may be advantageous to apply a suitable intermediate layer. Suitable intermediate layers are for example the aqueous 2-component polyurethane binders described according to the teaching of DE-A 197 15 427.
Since the coating composition cures already at room temperature, materials or objects can also be coated that cannot or must not be exposed to an elevated temperature. This is the case, for example, with the use of the coating composition according to the invention as an anti-fouling coating or with its use as an anti-graffiti coating that has not been applied at the factory. But the coating may also be cured in accelerated manner at elevated temperature. When the coating composition applied has hardened, the surface to be protected is highly hydrophobic and has effective nonstick properties. As a result, not only do the graffiti not adhere at all or only very poorly to the underlying surface, thus reducing their attractiveness to paint-sprayers, but they can also be removed in a residue-free manner both by graffiti-removing agents and with water using a high-pressure cleaning device. The surfaces coated with the coating compositions according to the invention are also effectively protected against damage from solvents, thereby prolonging the intervals between maintenance work. By reason of the low solvent content in comparison with the state of the art, the coating composition may also be used in many fields in which VOC guidelines restrict the solvent content. Application of the coating composition according to the invention may be effected by the conventional methods, such as spraying, brushing, dipping, flow coating, spin coating or blade coating.